Just picked up a 1930s Battery operated Coronado - Page 8 - Videokarma.org TV - Video

old_tv_nut · #**106** 01-04-2021, 12:08 PM

A frequency counter is much more precise at measuring frequency than a scope, so the counter could be used to calibrate the frequency of the signal generator, and then the signal generator could be used to calibrate the scope sweep time. Doing the opposite order would result in much larger errors.

old_tv_nut · #**107** 01-04-2021, 12:11 PM

Note that later and more expensive scopes may have built in measurement cursors to get a more precise measurement of time/frequency than just eye-balling the display, but eventually these have to be calibrated against a standard frequency source.

Really modern scopes are all digital sampling types, and the sampling rate is crystal controlled, so the scope really contains a calibrated reference.

vortalexfan · #**108** 01-04-2021, 12:46 PM

Quote:

Originally Posted by old_tv_nut

Note that later and more expensive scopes may have built in measurement cursors to get a more precise measurement of time/frequency than just eye-balling the display, but eventually these have to be calibrated against a standard frequency source.

Really modern scopes are all digital sampling types, and the sampling rate is crystal controlled, so the scope really contains a calibrated reference.

Ok, that makes sense. Thanks for explaining that to me.

vortalexfan · #**109** 01-08-2021, 06:12 PM

OK, so a little update: This radio had been working like a champ for the past week and a half and then today I was listening to it and the stations were bleeding over onto each other on the upper end of the dial and so I turned it off and went to turn it back on to see if it had cleared up the issue and for some reason or another I can't get it to turn on anymore, and I noticed that the power switch was a little finicky sometimes and would require me to turn the power knob a couple of times before it would finally turn on, but now its not turning on at all period except for a little crackling noises when I would turn the power switch on and off several times and then turn it on and wait for it to warm up, but I'm not getting any audio.

I'm thinking its the power switch, because I have a Philco 116B that's done the same thing with its power knob, except instead of sticking in the off position like this one seems to be doing it sticks in the on position.

and the switch that this farm radio uses has 2 sets of contacts in it rather than one set like your traditional AC power switches, one set of contacts is for powering on the B+ power and one is for turning on the A+ (Filiment) power and I'm not sure where I would get a new switch like that or if I could take the switch apart and clean the contacts and lubricate them and see if I could get the switch freed up and working again.

And no its not the batteries because I just installed a set of freshly recharged "D" batteries in the "A" Battery pack and the "B" batteries are still putting out a solid 89.5 Volts DC.

Any help would be appreciated.

Thanks!

init4fun · #**110** 01-08-2021, 06:30 PM

Your next step should be to disconnect the A and B wires from the switch (with the batteries disconnected) and connect the A and B supply's wires together in the proper way that the switch connects them when it's on . Then reconnect the batteries . If the radio plays , your switch is bad . If not , your gonna be looking for other problems .

vortalexfan · #**111** 01-09-2021, 01:22 AM

Quote:

Originally Posted by init4fun

Your next step should be to disconnect the A and B wires from the switch (with the batteries disconnected) and connect the A and B supply's wires together in the proper way that the switch connects them when it's on . Then reconnect the batteries . If the radio plays , your switch is bad . If not , your gonna be looking for other problems .

So how do I do that?

Electronic M · #**112** 01-09-2021, 02:12 PM

Quote:

Originally Posted by vortalexfan

So how do I do that?

He explained everything except how to figure out which wires to bridge together. That you do either by looking at the schematic and tracing the wiring (which I recommend) or by checking switch terminal resistance with the switch on and off. (These methods should be fairly obvious to anyone who has been working on electronics for a while and knows how to read a schematic)

Personally I wouldn't bother disconnecting leads from the switch(though you could go through the extra effort if you want) unless the 2 poles of the switch that aren't supposed to have continuity are shorting.... what I'd do is either jumpper the contacts at the terminals with clip leads or tack solder jumper wires across the correct terminals.

vortalexfan · #**113** 01-09-2021, 02:20 PM

Quote:

Originally Posted by Electronic M

He explained everything except how to figure out which wires to bridge together. That you do either by looking at the schematic and tracing the wiring (which I recommend) or by checking switch terminal resistance with the switch on and off. (These methods should be fairly obvious to anyone who has been working on electronics for a while and knows how to read a schematic)

Personally I wouldn't bother disconnecting leads from the switch(though you could go through the extra effort if you want) unless the 2 poles of the switch that aren't supposed to have continuity are shorting.... what I'd do is either jumpper the contacts at the terminals with clip leads or tack solder jumper wires across the correct terminals.

What I meant was do I connect wires together to bypass the switch altogether or do I connect the wires together and use the switch as well?

I guess I should of been clearer, but I was in a hurry last night.

Electronic M · #**114** 01-09-2021, 03:16 PM

Quote:

Originally Posted by vortalexfan

What I meant was do I connect wires together to bypass the switch altogether or do I connect the wires together and use the switch as well?

I guess I should of been clearer, but I was in a hurry last night.

If you have shorted the wires into the on mode such that the set will be on regardless of the switch position as he suggested, then whether or not you use the effectively bypassed switch is irrelevant.

The idea is that the switch acting up and the reception issues could be unrelated or the former could be causing the latter...ie the switch could have resistance sufficient to reduce filament or B+ voltage that could potentially cause reception issues.

If you bypass the contacts with a short and run the set you will learn if it reception problems were caused by switch contacts developing resistance.

vortalexfan · #**115** 01-09-2021, 03:35 PM

Quote:

Originally Posted by Electronic M

If you have shorted the wires into the on mode such that the set will be on regardless of the switch position as he suggested whether or not you use the effectively bypassed switch is irrelevant.

OK well I didn't understand that that was what he was saying.

But anyways I was just kind of monkeying around with the radio a little bit and I just turned the knob on just now and it came on just fine today on the first try which is weird because last night I couldn't get it to do anything.

I'll still try out what you said as far as trying to bridge the A and B wires together and see what that does.

but as far as which wires to bridge as I said if you look at the schematic and the switch wiring, it has four terminals on the switch, one is wired to the "A" Battery supply (Red Wire from the "A" Battery supply Pack) and the other one is wired to the "B" battery supply (the blue wire from the 10 9V batteries wired in series), and then the other two terminals are wired across the filiment string and the the B+ rail respectively, So I take it I would have to just put a jumper between the two "A" Supply switch terminals and the two "B" supply Terminals on the switch in order to bypass the switch?

See the schematic posted below.

old_coot88 · #**116** 01-09-2021, 03:55 PM

Quote:

Originally Posted by vortalexfan

...So I take it I would have to just put a jumper between the two "A" Supply switch terminals and the two "B" supply Terminals on the switch in order to bypass the switch?

Yuppers.

vortalexfan · #**117** 01-09-2021, 04:02 PM

Quote:

Originally Posted by old_coot88

Yuppers.

Ok, that's what I was thinking but I wasn't sure, that's why I was asking.

vortalexfan · #**118** 01-10-2021, 10:41 PM

OK so, an update: Its NOT the switch, its something else causing this thing to act up, because I took the switch apart on this radio and sprayed some WD40 into the switch and worked it around and checked the switch and it definitely opens and closes the circuit like its supposed to when the switch is in the on and off position.

So I put the switch back together and put the radio back together, and then let it sit for a little bit and then put the batteries back into the set and then turned it on and the radio came on like it was supposed to.

I listened to the radio for about 15 or 20 minutes and then suddenly the radio just died, it didn't fade out or slowly die it just immediately cut out with a slight "pop", almost like someone had turned the radio off with the power switch, but I hadn't touched it.

Any ideas as to what the problem could be?

vortalexfan · #**119** 01-10-2021, 11:07 PM

Disregard previous post, I figured out what the problem was, it was a faulty 9V Battery in my "B" Battery setup.

dieseljeep · #**120** 01-11-2021, 10:53 AM

Quote:

Originally Posted by vortalexfan

Disregard previous post, I figured out what the problem was, it was a faulty 9V Battery in my "B" Battery setup.

I've been following this thread from the very beginning. I would knock together a simple B+ supply using a silicon rectifier or bridge rectifier, two 20mfd electrolytics , 2200ohm, 1 watt resistor and 180 ohm, 1 watt before the rectifier.
Once you get all the problems straightened out, you can go back to using battery power.
I built one 65 years ago because of the high cost of "B" batteries.
Flashlite cells were only 15 to 25 cents at the time.